A primary task of the heart is to pump oxygenated, nutrient-rich blood throughout the body. Electrical impulses generated by a portion of the heart regulate the pumping cycle. When the electrical impulses follow a regular and consistent pattern, the heart functions normally and the pumping of blood is optimized. When the electrical impulses of the heart are disrupted (i.e., cardiac arrhythmia), this pattern of electrical impulses becomes chaotic or overly rapid, and a Sudden Cardiac Arrest may take place, which inhibits the circulation of blood. As a result, the brain and other critical organs are deprived of nutrients and oxygen. A person experiencing Sudden Cardiac Arrest may suddenly lose consciousness and die shortly thereafter if left untreated.
The most successful therapy for Sudden Cardiac Arrest is prompt and appropriate defibrillation. A defibrillator uses electrical shocks to restore the proper functioning of the heart. A crucial component of the success or failure of defibrillation, however, is time. Ideally, a victim should be defibrillated immediately upon suffering a Sudden Cardiac Arrest, as the victim's chances of survival dwindle rapidly for every minute without treatment.
There are a wide variety of defibrillators. For example, Implantable Cardioverter-Defibrillators (ICD) involve surgically implanting wire coils and a generator device within a person. ICDs are typically for people at high risk for a cardiac arrhythmia. When a cardiac arrhythmia is detected, a current is automatically passed through the heart of the user with little or no intervention by a third party.
Another, more common type of defibrillator is the automated external defibrillator (AED). Rather than being implanted, the AED is an external device used by a third party to resuscitate a person who has suffered from sudden cardiac arrest. FIG. 8 illustrates a conventional AED 800, which includes a base unit 802 and two pads 804. Sometimes paddles with handles are used instead of the pads 804. The pads 804 are connected to the base unit 802 using electrical cables 806.
A typical protocol for using the AED 800 is as follows. Initially, the person who has suffered from sudden cardiac arrest is placed on the floor. Clothing is removed to reveal the person's chest 808. The pads 804 are applied to appropriate locations on the chest 808, as illustrated in FIG. 8. The electrical system within the base unit 800 generates a high voltage between the two pads 804, which delivers an electrical shock to the person. Ideally, the shock restores a normal cardiac rhythm. In some cases, multiple shocks are required.
Although existing technologies work well, there are continuing efforts to improve the effectiveness, safety and usability of automatic external defibrillators.
Accordingly, efforts have been made to improve the availability of automated external defibrillators (AED), so that they are more likely to be in the vicinity of sudden cardiac arrest victims. Advances in medical technology have reduced the cost and size of automated external defibrillators (AED). Some modern AEDs approximate the size of a laptop computer or backpack. Even small devices may typically weigh 4-10 pounds or more. Accordingly, they are increasingly found mounted in public facilities (e.g., airports, schools, gyms, etc.) and, more rarely, residences. Unfortunately, the average success rates for cardiac resuscitation remain abysmally low (less than 1%).
Such solutions, while effective, are still less than ideal for most situations. Assume, for example, that a person suffers from a cardiac arrest in an airport in which multiple AEDs have been distributed. The victim's companion would nevertheless have to locate and run towards the nearest AED, pull the device off the wall, and return to the collapsed victim to render assistance. During that time, precious minutes may have passed. According to some estimates, the chance of surviving a sudden cardiac arrest is 90% if the victim is defibrillated within one minute, but declines by 10% for every minute thereafter. A defibrillator design that reduces the time to defibrillation by even two to three minutes will save more lives.
An additional challenge is that a sudden cardiac arrest may take place anywhere. People often spend time away from public facilities and their homes. For example, a sudden cardiac arrest could strike someone while biking in the hills, skiing on the mountains, strolling along the beach, or jogging on a dirt trail. Ideally, an improved AED design would be compact, light, and resistant to the elements and easily attached or detached from one's body. The typical AED design illustrated in FIG. 8, which includes a sizable console or power unit whose form factor is similar to that of a laptop or backpack, seems less than ideal for the outdoors and other rigorous environments.
New and improved designs are allowing AEDs to become ultra-portable and hence to able to be easily carried by an at-risk person as they go about all of their daily activities and thus are able to be close at hand when a sudden cardiac arrest strikes outside of a hospital environment or a high traffic public area with a Public Access Defibrillator.
There are also improvements being made in the area of device usability and ease of operation for untrained bystanders. As noted above, every minute of delay or distraction can substantially decrease the victim's probability of survival. As a result, it is generally beneficial to streamline the operation of the external defibrillator so that a user of the defibrillator, who is presumably under substantial mental duress, can focus his or her attention on a few key variables.
Another type of defibrillator is the Wearable Cardioverter Defibrillator (WCD). Rather than a device being implanted into a person at-risk from Sudden Cardiac Arrest, or being used by a bystander once a person has already collapsed from experiencing a Sudden Cardiac Arrest, the WCD is an external device worn by an at-risk person which continuously monitors their heart rhythm to identify the occurrence of an arrhythmia, to then correctly identify the type of arrhythmia involved and then to automatically apply the therapeutic action required for the type of arrhythmia identified, whether this be cardioversion or defibrillation. These devices are most frequently used for patients who have been identified as potentially requiring an ICD and to effectively protect them during the two to six month medical evaluation period before a final decision is made and they are officially cleared for, or denied, an ICD.
External Defibrillators and Automated External Defibrillators on the market today make use of either rigid paddles that must be held in place on the patient's body or else flexible electrode pads (made of conductive foil and foam) which are stuck to the patient's skin. The current external defibrillators that have rigid paddle bases do not conform to the curvatures of the patient's body at the locations on the body where the paddles must be placed in order to be effective. As such the operators of these devices must apply a good amount of contact force to make physical contact across the paddle's patient contact interface and must maintain this force to maximize the surface area in contact with the patient for the sensing and reading of the heart rhythm in order that the device can detect the presence of a faulty rhythm, or arrhythmia, such as Ventricular Fibrillation or Ventricular Tachycardia so as to instruct/initiate or signal the external defibrillator to deliver the life saving therapeutic defibrillation shock pulse. The operator must also continue holding the required contact force while the device delivers the chosen therapeutic action (shock or no shock).
There are medical, practical and commercial needs to make new AEDs which are smaller, potentially even flexible, and hence much more discrete in order for patients to be able to carry the devices around with them as they go about their daily lives. This means that the life saving device is always with them for a bystander to use immediately if they drop from a Sudden Cardiac Arrest. This is far preferable to the current system of having a few AEDs mounted on the walls of a limited number of the most high traffic public locations.
Wearable Cardioverter Defibrillators on the market today are still bulky and uncomfortable for the patients to wear. They utilize a single source of energy in a box that attaches to the wearable garment (containing the sensors and the electrodes) and the energy source box normally rides on the hip. These are heavy and uncomfortable to wear and a frequent source of complaints from patients.
Current Wearable Cardioverter Defibrillators have fixed flat surface electrodes and fixed curved surface electrodes for positioning on the patient's back and abdomen. This requires that each patient has to be specially fitted for their own unit, which is time consuming for the patient. Given the limited range of device sizes available it also requires that the device be worn tightly in order to maintain a constant contact pressure with both the sensors and the electrodes, which is restrictive and can be uncomfortable for the patient. This is also the reason why the devices also employ the use of liquid conductive hydrogel, to ensure that the electrode-to-patient contact impedance is minimized. This is messy to clean up after each use when deployed by the device, and naturally this can adversely impact the patient's clothing. It also requires that the liquid reservoirs be recharged before the device can be effectively used again.
There are medical, practical and commercial needs to make new WCDs smaller and more flexible, more comfortable and more discrete for patients to wear as they go about their daily lives.